Object presence detection method and device

ABSTRACT

An object presence detection device, of the type mounted to a motor vehicle having at least one blind spot, where the detection device is for detecting an object situated in the blind spot, comprises: a receiver for detecting electromagnetic waves, comprising a focussing device, and a light detector converting said received electromagnetic waves into electrical signals; an electronic circuit converting the electrical signals into digitized signals; a logic circuit analyzing the digitized signals to analyze the presence of objects in the blind spot which are moving relative to the vehicle, and emitting variable output signals depending on the result of the analysis; indicator members activated by the output signals, suitable to be perceived by the driver.

FIELD OF THE INVENTION

The invention relates to an object presence detection method and to adevice to put said method into practice, the device being of the typemounted to a motor vehicle having at least one blind spot, where thedetection device is for detecting an object situated in the blind spot.

BACKGROUND OF THE INVENTION

Conventional motor vehicles are usually provided with rear view mirrors,generally one internal mirror and one or two external mirrors, whichallow the user or driver to see behind without the user having to turnhis or her head around. Nevertheless, in spite of having a plurality ofmirrors there are usually areas, known as blind spots, which are notcovered by said mirrors.

There is known the use of systems, which capture an image orientedtowards a blind spot by means of a CCD camera and show it to the user ona screen located in the vehicle passenger compartment. These systemsmake it possible for the user to see in the blind spots without havingto move himself, nevertheless, they have a number of drawbacks: theyrequire image transmission systems having a sufficient quality for theuser to perceive a clear picture, which requires working with a highnumber of pixels, there must be space in the passenger compartment to beable to accommodate the corresponding screen, the system does notprocess the image but only transmit it, etc. They are, therefore,expensive systems, which do not cooperate actively in the detection ofsituations of risk.

SUMMARY AND OBJECTS OF THE INVENTION

It is an object of the invention to overcome some drawbacks andlimitations of the mentioned prior art. This object is achieved by anobject presence detection device of the type first mentioned above,which comprises: (a) a receiver for detecting electromagnetic waves,comprising a focussing device, and a light detector converting thereceived electromagnetic waves into electrical signals, where the lightdetector defines an image surface, (b) an electronic circuit convertingthe electrical signals into digitized signals, (c) a logic circuitanalyzing the digitized signals to analyze the presence in the blindspot of objects which are moving relative to the vehicle, and generatingvariable output signals depending on the result of the analysis, (d)indicator members, activated by the output signals, suitable to beperceived by the driver, the passenger or, in general, by any passengerof the vehicle.

In fact, a detection device of this type captures the blind spot imageand analyzes it, informing the driver of the result of the analysis.This affords a number of advantages: the driver is now shown the blindspot image, whereby it is not necessary to have space in the compartmentfor a screen, the driver is additionally provided with information of“greater value” in the sense that the detection device has alreadyeffected an analysis and the driver or user is provided with the resultof the analysis. Furthermore, the detection device requires receiverswith a smaller number of pixels than required to provide the driver withan image of the blind spot having a minimum quality, whereby thedetection device may be equipped with cheaper receivers without any lossof performance.

The detection device not only analyses the presence of an object in theblind spot, but also provides a qualitative idea of the speed of theobject relative to the vehicle and, therefore, determines whether theobject is approaching or receding, with an approximate idea of thespeed. This allows fuller information to be provided to the driver,since he may distinguish different levels of risk depending on therelative speed of the object.

The detection device also provides a qualitative idea of the distance ofthe object relative to the vehicle and, therefore, determines theposition of the object relative to the vehicle. This allows fullerinformation to be provided to the driver, since he may distinguishdifferent levels of risk depending on the position of the object.

The light detector is preferably a set of sensor elements, which areadvantageously photodiodes, distributed according to a flattwo-dimensional matrix defining mutually parallel rows. In this way, thesensor element matrix defines the image surface, which is formed by aplurality of pixels, where one sensor element corresponds to each pixel.

The photodiodes convert the electromagnetic waves into an electricalcurrent. This electrical current is preferably converted to anelectrical voltage and is amplified.

The light detector is preferably formed by active sensor elements havinga dynamic range of not less than six decades (10⁶=120 dB) on one sameimage surface, i.e., between the minimum detection threshold value andthe saturation threshold there is a range of six decades, with the lightintensity being expressed in lux. Likewise, a pixel which are any onetime is receiving the minimum detection value, may detect in thefollowing image acquisition a value six decades greater, and vice versa.This allows the receiver to operate in a variety of light conditions,and even under adverse light conditions, with powerful light contrasts,such as when driving at night. It is for the same reason preferable thatone same sensor element should have a dynamic range equal to or greaterthan six decades between two consecutive images.

The electronic circuit is preferably capable of selecting each of saidsensor elements by activating the corresponding row and thecorresponding position in said row, it thus being possible to select anysensor element subsequent to any sensor element. In this way, theelectrical signal from each of the sensor elements may be taken and allthe pixels forming the image surface may be sequentially amplified anddigitized. Alternatively, it is also possible for the electronic circuitto simultaneously convert all the electrical signals from a row ofsensor elements to digitized signals. Thus, in each particular design,the higher cost of this solution relative to the greater speed ofdigitization of the image must be evaluated.

As stated above, one of the objects of this invention is to be able touse receivers fitted with low-cost light sensors. It is, in this sense,preferable that the sensor element matrix should have 512×512 sensorelements at the most, and it is most preferred that the maximum numberbe 320×256 sensor elements. In general, these values relate to thenumber of active sensors for processing the image. In other words, thesensor element matrix may have more sensor elements, but which are notactivated for image processing.

Once the image has been digitized the logic circuit analyzes the imagesurface. To this end, there is carried out a mathematical convolutionpreferably, particularly a convolution kernel appropriate for adetection of movement, along the entire image surface of the digitizedsignal or along a portion thereof.

The logic circuit preferably comprises a specialized electronic circuitthat includes: [a] a Von Neumann type sequential central processing unit(CPU), [b] a parallel coprocessor, specialized in the calculation of theconvolution over the entire image surface, and which includes at least32 parallel accumulator multipliers with a high calculation speed forcalculating the convolution directly on the image surface at such acalculation speed that the convolution is completed before a new imageacquisition is initiated, and [c] a local RAM. In particular it ispreferable that the calculation speed is such that it allows aconvolution to be calculated in a time of less than 100 ms.

Preferably the detection device is adapted to distinguish a vehicle fromother objects. This is achieved, for example, by recognizing edges orarrises, forming rectangles with said edges and comparing saidrectangles with a set of patterns. When it has detected a vehicle, itanalyzes the relative speed between the detected vehicle and the vehiclefitted with the detection device from the following image.

A preferred embodiment of the invention contemplates dividing the imagesurface into at least two portions, and using different analysistechniques on each of said portions. Thus, in one of said portions thetechnique is the one already indicated in the foregoing paragraph, thatis to say, in the recognition of the edges, the formation of rectangles,the comparison of the rectangles with a set of patterns and thecomparison of two consecutive images to calculate the relative speed,while in another portion a technique is used based on a phase differenceto obtain an estimate of the optical flow in a particular direction, tobe precise in the direction of the street or road on which the vehicleis moving.

Another analysis technique consists of detecting vertical and/orhorizontal arrises clearly marked on the image of the road.Advantageously this technique also includes the follow-up, throughsuccessive images, of the movement of said arrises, and the calculation,from said follow-up, of the relative speed of the object (vehicle)detected to the vehicle fitted with the detection device. This techniqueis described later on in greater detail.

It is also possible that more than one analysis technique may be usedsimultaneously in one or more of the portions into which the imagesurface has been divided.

In general, the detection device should give a warning signal ondetecting a situation in which there is a collision risk. This signalshould serve to give the driver time to avoid or correct a dangerousmaneuver. In this sense it is evident that the warning signal should beactivated sufficiently in advance for the driver to be able to reactappropriately. On considering a situation in which a vehicle enters amotorway, which represents an extreme situation regarding the relativespeed between the incoming vehicle and the vehicles driving on themotorway, it will be understood that the detection device should have awide action radius, to be able to warn the driver sufficiently inadvance. Thus, it is preferable that the radius of action of thedetection device be greater than 15 m, or better still, greater than 20m. In this sense, the detection device covers a wider field of visionthan strictly the blind spot. Thus, the detection device can detectsituations of risk and alert the driver even when the situation of riskwas detectable through the rear-view mirror. Thus the cooperation of thedetection device in safe driving of the vehicle is much more extensive.

The focussing device can comprise any usual optical element, which isobvious to one of ordinary skill in the art. In particular, it can havea lens or a microlens integrated in the integrated circuit including thefocussing device. It is also possible to include an electromagnetic wavetransmission guide. This would allow, for example, the whole detectiondevice to be placed at any place inside the vehicle, and to be connectedto the outside through said guide. However, the small dimensions of thedetections device allow it to be placed inside a rear-view mirror, whichis a preferred embodiment, or it is even possible to place a detectiondevice in each of the external rear-view mirrors of a vehicle.

To achieve small sizes, at the same time as low consumption rates and asimplification in the communications between the different components ofthe detection device, it is advisable that the electronic circuit andthe light detector are of CMOS, DMOS, MOS, Si-Ge, BiCMOS technology orSOI (silicon on insulator) technology, and that the light detector andthe electronic circuit are physically connected in a multi-chip module(MCM) on a plastics material, fiber glass (FR4), ceramic or siliconsubstrate.

Optionally the capacity of the detection device to analyze thesituations of risk may be improved if, to the characteristics ofdetection of an approaching object, there is added the capacitydetecting whether the vehicle on which the detection device is mountedhas initiated actions indicative of an approach to the object. Inparticular, it is advantageous that the detection device be able todetect the actuation of an indicator and/or be able to detect a turn ofthe vehicle steering wheel.

If is also of interest that the detection device should be able tocommunicate various signals to the user or driver of the vehicleallowing the warning signal to be graduated depending on the collisionrisk. It is thus preferred that the indicative elements include luminoussignals having at least two colors, where each color indicates adifferent warning level. It is also advantageous to include an outputelement allowing the pictograms to be shown, where said output elementis a matrix of LED's or a graphic screen.

A situation of risk may also occur if a passenger of the vehicle fittedwith the detection device opens a door without checking whether anothervehicle is approaching from behind. It is, therefore, advantageous thatthe detection device also indicates said situations of risk to thevehicle's passengers.

It is advantageous to allow the detection device to act on the doorlocks. Thus, for example, it can block a door if it detects a situationof risk.

Finally it is advantageous to add to the object presence detectiondevice a device for detecting drowsiness of the driver. Preferably thedrowsiness detection device shares most of the physical devices with theobject presence detection device and emits an alarm signal depending onthe relative position of the vehicle fitted with the detection device tothe lines marking the lanes on the road surface.

Further advantages and features of the invention will be appreciatedfrom the following description wherein, without any limiting nature,there is described one preferred embodiment of the invention, withreference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1D show an outline of the blind spots of a vehicle, the areasof direct vision and through the left rear-view mirror, and the areacovered by a detection device according to the invention.

FIG. 2 is a simplified diagram of a detection device according to theinvention.

FIG. 3 is a front elevation view of a rear-view mirror showing fivepossible locations of the receiver.

FIG. 4 is a diagram of an image surface.

FIG. 5 shows the image surface of FIG. 4, divided into three portions,and

FIG. 6 is a block diagram of an algorithm according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

by way of example, FIGS. 1A to 1D schematically illustrate the areasvisible through the left side (driver's side) rear-view mirror 1, theareas visible as a result of the driver's lateral peripheral vision 3,and the blind spots 5. The areas visible through the rear-view mirrors 1must comply with a number of legal requirements, for example thosedefined in E.C. Directive 71/127 and in the following directives. Inparticular, as shown in FIG. 1A, the angle of vision should be such thatat a distance of 10 m from the rear-view mirror, the width of the areaseen should be at least 2.5 m. In FIG. 1A there is to be seen a hatchedrectangular area corresponding to the legal requirement, and atriangular area corresponding to what is really seen through aconventional rear-view mirror satisfying the legal requirement.

It is precisely these blind spots 5 that the detection device of thepresent invention is intended to cover. The detection device should,furthermore, partially overlap with the area seen in the rear-viewmirror, in order to avoid discontinuities between what the sensordetects and what the driver sees. For this same reason it is desirablethat the sensor should also cover part of the area seen directly by thedriver. In this sense, one possible solution consists of using adetection device that covers an area such as the shaded one in FIG. 1C:a right angle triangular shaped area the sides of which are both 4.5 mfollowed by a rectangular area 4.5 m wide. The total length of thecovered area may be made to depend on the capabilities of the detectiondevice. By way of example, FIG. 1C shows a range of 20 m, although thedetection device described hereinafter has a range of more than 20 m.

FIG. 1D is a combined illustration of all the previous area together. Itwill be seen that the blind spot is practically entirely covered, as faras the area corresponding to the adjacent lane is concerned. There isalso an overlap with the areas seen directly or through the rear-viewmirror.

The detection device of the invention shown in FIGS. 2 to 5 comprises areceiver 7 that it is formed by a matrix of 256 rows of photodiodes,with 320 photodiodes in each row. The receiver 7 receives theelectromagnetic waves coming from the exterior, in this particular caseinside the range of the visible light, suitably focused thanks to alens. When the light impacts of the photodiodes, these generate anelectrical current, the intensity of which depends on the intensity ofthe light received. This electrical current is converted into a voltage.By selecting a row and a position inside the row, it is possible toselect a photodiode, which thus transmits the electrical signal to anelectronic circuit 9. The electronic circuit 9 is provided with anamplifier stage 11, and an analog-digital conversion unit ADC, whichoutputs a digitized signal.

The digital signal is fed into a logic circuit 15. The logic circuit 15comprises a Von Neumann type sequential central processing unit CPU, aparallel coprocessor TOT that calculates the convolution and is based onan auxiliary memory MEM, a FLASH memory and rapid access static RAM(SRAM). The central processing unit CPU also controls the receiver 7,sending the row selection signals 17 and position inside the row signals19 to the corresponding registers, and to the electronic circuit 9.

The receiver 7 picks up an image, including the blind spot that isprojected on the image surface formed by the photodiodes. It is thisimage surface which is transmitted to the logic circuit 15 in form of anumber of digitized pixels. The receiver 7 is orientated in such a waythat the side edge of the image surface is practically flush with theside surface of the motor vehicle 21 and the upper edge of the imagesurface is flush with the horizon 23. The logic circuit 15 determinesthe direction of movement along the street or road, which allows it todetermine whether a detected movement is in the direction of the road orif it is in another direction, for example vertical. Thus it can filter“noises”, such as may be rain, snow, vehicles moving in the oppositedirection, etc.

FIG. 3 shows some examples of positioning of the receiver 7 or, in thecase may be, of the end of the electromagnetic wave guide, in anexternal rear-view mirror.

As has already been indicated previously, various image analysisalgorithms may be affected. In one case the image surface is divided intwo portions 25, 27 having an overlap area 29, as shown in FIG. 5. Thelogic circuit 15 has two independent algorithms: a vehicle detectingalgorithm that is applied in portion 25, and a movement detectingalgorithm that is applied in portion 27. Both algorithms are applied inthe overlap area 29. The vehicle detecting algorithm recognizes theedges of figures existing on the image surface, selects the horizontallyand vertically disposed edges and is compared with certain patterns todetermine whether there is an object having a shape similar to that of avehicle. In the affirmative, the next image obtained by the receiver 7is analyzed, which allows the direction of the movement, as well as thespeed of the object, to be determined. The movement-detecting algorithmis based on a phase difference technique to obtain an estimate of theoptical flow in the direction of the road. The result is compared withthe results obtained in previous images, to eliminate errors and noisesby means of a consistency check.

Another possible image analysis algorithm is based on the following. Asalready said above, the device is designed to detect vehicles overtakingthe vehicle fitted with the device by means of the series of imagescaptured with a digital camera, for example a CMOS camera, mounted inthe rear-view mirror of a vehicle.

The presence of an approaching vehicle is based on the detection andfollow-up of objects moving along the axis of the road (in general anypublic way) and drawing closer to the vehicle fitted with the device.Starting from an image, the presence of a vehicle may be appreciated bythe presence of arrises (or edges) clearly marked in the vertical andhorizontal directions on the road surface. In successive images thesevisual elements (the vertical and horizontal arrises) move forwardly ifthey are part of an approaching vehicle. On the contrary, they movebackwards if they are part of static objects (such as elements of thehighway, protective barriers, trees, traffic signals, milestones, etc.)or if they belong to vehicles moving the opposite direction to thevehicle fitted with the device. Therefore a coherent forward movement isinterpreted as an overtaking vehicle.

This interpretation is generally correct on motorways or similar roads,where the lanes are clearly defined and the curves usually have a largeradius. In these cases the image is a simple perspective view and theovertaking lane can be isolated in a simple way from the rest of thescene using an appropriate mask. Therefore, a forward movement in theovertaking lane is a clear indication of an approaching vehicle. Noisesand interference due to holes in the road or abrupt movements of thevehicle fitted with the device can be eliminated by requiring that theforward movement be coherent through various successive images.

The visual image on a road that is not a motorway or the like is muchmore complex. In particular, the turns to the left of the vehicle fittedwith the device can generate a consistent apparent movement, which maygenerate false alarms. This is particularly frequent in urbanenvironments, where the visual scene contains a large number of objects(parked cars, buildings, diverse traffic signs, etc.) having markedarrises. Furthermore the true distance between the approaching vehicleand the vehicle fitted with the device cannot be correctly estimatedfrom its position, since the lanes are not clearly defined. For thisreason it is desirable that the detecting device should have a specificoperation module for when the device-carrying vehicle is turning to theleft. Thus, during a turn to the left, the detection field moves to aposition closer to the vehicle fitted with the device and morerestrictive requirements are imposed before activating the alarm signal.As consequence the alarm signal will be activated when the approachingvehicle is closer to the vehicle fitted with the device. However this isnot a problem because around tight curves the vehicle speeds are slowerthan on motorways or other fast roads. Furthermore, in view of theconfiguration of the street and the frequent presence of intersections,a long detection range is not necessary in the case of an urbanenvironment.

As a particular example the camera may be provided with a sensor that isa 320×256 CMOS matrix with a high dynamic range (120 dB). The size ofthe processed images is at least 128×128 pixels. The field of vision ofthe camera is approximately 55°. The camera is positioned in such a waythat:

-   -   the left vertical edge of the image is close to the side edge of        the vehicle fitted with the device.    -   the upper edge of the image is slightly above the horizon line,        by approximately one eighth of the image.    -   the camera is slightly tilted in the clockwise direction so that        it aligns the image along the axis of the highway.

A mask is used that is controlled from the software that defines theregion of interest of the images. The mask is positioned in such a waythat a car located in the overtaking lane of a straight road and at agreat distance is positioned in the left upper end of the mask. Theposition of the mask in the image can be adjusted to get a fineadjustment of the field of vision.

So that the detection device may work appropriately the image capturespeed should preferably be in excess of 40 images per second, since inthis way the device is capable of following the trajectory of theapproaching vehicles with greater accuracy. The detection devicealgorithm has four main modules basically:

An optical flow detection module. The algorithm uses a technique basedon phase differences to produce a dense estimate of the optical flow inthe direction of the axis of the road. To this end a pair of successiveimages is processed. Visual elements that are not moving forward arefiltered and eliminated. The resulting images are fed to the followingmodules. This module is optional and may be not used.

Vehicle detection and follow-up module. In the region defined by themask the algorithm calculates the arrises of the image and theirdirections. The vertical arrises and the horizontal arrises arenormalized and integrated along the vertical and horizontal axesrespectively. The normalization factor is adjusted dynamically based onthe average density of the arrise. The unidirectional projection of saidarrises on the corresponding coordinates axis is used to trace thetrajectory according to said axis. Approaching objects generateprojections with positive speeds, that is to say to the right anddownwardly of the image. These points are separated from other pointsthat are stationary or have relative movements with the aid ofdirectional filters. The resulting trajectories are identified andselected.

Module for detection of vehicles without relative speed. Once thetrajectory of an approaching vehicle has been identified (by means ofthe displacement of its corresponding unidirectional projections) thespeed of the vehicle is estimated and supervised. Therefore it ispossible to detect situations in which this approaching vehicle reducesspeed and circulates at the same speed as the vehicle fitted with thedevice, staying at a short distance from the vehicle fitted with thedevice. In these cases it is possible to emit a specific type of alarmsignal until substantial changes (dropping behind or overtaking thevehicle fitted with the detection device) are observed in theenvironment of the image of the approaching vehicle. In other words,this module allows for control of traffic situations (for example densetraffic) where parallel circulation takes place, namely, vehiclescirculating in different lanes at practically the same speed. In thesecases it is relatively frequent for a vehicle to be positioned in theblind spot of another vehicle, which may generate situations of danger.

Left turn detection module. During left turns, there occurs a constantoverall displacement of the visual elements contained in differentimages. The constant displacements are detected in the upper portion ofsuccessive images by means of a correlations technique. The coherence ofthis signal during a number of successive images is used as anindication that the vehicle fitted with the device is turning and,therefore, that the left turn detection module should be activated.

FIG. 6 shows a block diagram in which the states of the algorithm areillustrated. The reference numbers given represent the following blocks:

6.1 Initialization of the algorithm

6.2 Image acquisition

6.3 Optical flow estimate

6.4 Left turn detecting

6.5 Vehicle detection and follow-up

6.6 Consistent forward movement?

6.7 Activate alarm

First of all, the optical flow module 6.3 carries out a coarse filteringof the image flow, basing itself on the direction of the movement. Then,the left turn module 6.4 wars the system whether the vehicle fitted withthe device is turning. Next the detection and follow-up system 6.5follows the trajectories of the moving objects and activates, ifrequired, the corresponding alarm signal. Next, if the alarm isactivated, the zero speed module is activated.

Two modes of operation may be established. If the vehicle fitted withthe device is not turning, only the projections of the trajectoriesalong the horizontal axis are considered. If the follow-up moduledetects a trajectory longer than 15 images, an alarm signal is generatedand it gives an estimate of the relative distance and the relative speedof the approaching vehicle. This indication is reliable in the case offlat, straight roads, such as motorways or the like.

If the left turn detector is activated the requirements for the alarm tobe activated are stricter: First the images are filtered using theoptical flow detector, in order to reduce the noise, and the twoprojections (along the vertical axis and along the horizontal axis) aretaken into consideration. Only if a visual effect is moving forward bothon the X axis and the Y axis is the alarm signal activated. This is donethis way, since during the turns the visual elements are characterizedby having a positive speed according to the X axis, but with anapproximately null speed according to the Y axis, the height thereof ismaintained. Additionally the position of the mask is lowered and movesto the right to cover the region of interest (the overtaking lane) ofthe images.

Then, the logic circuit, depending on the information obtained (vehiclepresence, distance of the vehicle, and relative speed) activates, forexample, a group of three different colored LEDs (red, amber, green)(not shown in the Figures), allowing it to communicate different warninglevels, depending on the danger. A plurality of ways of presenting thewarning levels is possible: from a single red luminous signal that isactivated to indicate the presence of a object in the detection area,through to complex devices, with diverse luminous, acoustic and tactilesignals.

The detection device has a range of more than 20 m. Thus, in thesituation previously indicated by way of example, in which a vehiclewants to enter a motorway, a case in which there may be relative speedsof the order of 120 km/h, the driver receives the warning signal withalmost 1 s of time.

Where the detection device is mounted simultaneously on two externalrear-view mirrors (one in each side of the vehicle), it is possible toadd thereto, additionally, a driver drowsiness detection device.Preferably the drowsiness detection device shares all the physicalelements of the object presence detection device that participate in thecapture and processing of images, such as the receiver, the electroniccircuit and the logic circuit. Additionally the drowsiness detectiondevice has an algorithm that allows drowsiness to be detected in the waydescribed herebelow.

By means of the images obtained through each of the object presencedetection devices disposed in each of the rear-view mirrors, the markinglines of the lane in which the vehicle fitted with the detection deviceis driving are detected. Thus it is possible to detect when the vehiclefitted with the device crosses one of said marking lines. Indeed, as aconsequence of drowsiness, the driver is no longer able to follow thelane, marked by the marking lines, and leaves it, creating a situationof danger. The drowsiness detector is capable, therefore, of detectingthis circumstance and of emitting an alarm signal.

To recognize said marking lines, the drowsiness detection deviceanalyzes the image in the region immediately behind the car, it extractsthe edges of the marking lines (the arrises thereof) and follows them intime. The distance between the wheel and the edge of the marking linecan be detected and it is thus possible to emit an alarm signal when thevehicle is about to cross over said line. Preferably the drowsinessdetection device is connected to the turn detection module, allowing itto identify the case in which the marking line is approached, becausethe vehicle is negotiating a curve. Also the drowsiness detection devicereceives information on the possible activation of the indicators,allowing it to discern a voluntary crossing of the marking lines from aninvoluntary or, at least, unnotified crossing.

If the drowsiness detection device detects an inadvertent crossing of amarking line, it activates a warning signal. This warning signal may betactile (for example vibrations in the steering wheel), luminous and/oracoustic.

It is also possible to make a drowsiness detection device from a singleobject presence detection device, disposed in a single rear-view mirror,although in this case it is likely that the benefits thereof, in thesense of the quality or relevancy of the warning signals it emits, willnot be the same.

The drowsiness detection device is always directed to the rear, andcovers exactly the same area of detection as the object presencedetection device, since it preferably shares therewith all the physicaldetection and calculation elements.

1. A method of object presence detection, by using a detection device ofthe type mounted to a motor vehicle, said vehicle having at least oneblind spot, where said detection device is for detecting an object suchas an approaching vehicle situated in said blind spot, comprising: (a) areceiver (7) for detecting electromagnetic waves, said receiver (7)comprising a focusing device, and a light detector including a set ofactive photosensor elements that converts said electromagnetic wavesinto electrical signals, said light detector defining an image surface,(b) an electronic circuit (9) converting said electrical signals intodigitized signals, (c) a logic circuit (15) analyzing said digitizedsignals to analyze the presence of objects in said at least one blindspot which are moving relative to said vehicle, and generating variableoutput alarm signals depending on the result of said analysis, and (d)indicator members activated by said output signals, said detectiondevice being adapted to distinguish a vehicle from other objects,wherein said distinguishing is effected by recognizing arrises, clearlymarked on at least a first portion of said image surface of interest invertical and/or horizontal directions on a road surface and thefollow-up of the movement of said arrises through various successiveimages to calculate a relative speed of a detected object providing saidarrises.
 2. A method, according to claim 1, wherein on a second portionof said image surface a different technique is used based on a phasedifference to obtain an estimate of an optical flow in one direction. 3.A method according to claim 1, wherein said recognition of arrises isperformed by said logic circuit (15) carrying out a mathematicalconvolution over at least said first portion of said image surface ofthe digitised signal thereafter distinguishing a vehicle from otherobjects.
 4. A method according to claim 3, wherein said mathematicalconvolution over at least said first portion of said image surface iscarried cut by means of a convolution kernel appropriate for a movementdetection.
 5. A method according to claim 3, wherein said convolution iscalculated in time no greater than 100 ms.
 6. A method, according toclaim 1, wherein: said portion of the image of interest is defined by amask controlled by software and in that an algorithm calculates thearrises of the image and their directions, said vertical and horizontalarrises being normalized and integrated along the vertical andhorizontal axes respectively; a normalization factor is adjusteddynamically based on average density of said arrises, usingunidirectional projection of said arrises on corresponding coordinatesaxis to trace a trajectory according to said axis so that approachingobjects generate projections points with positive speeds, and saidprojection points are separated from other points that are stationary orhave relative movements with the aid of directions filters finallyidentifying and selecting the resulting trajectories.
 7. A methodaccording to claim 6, wherein: once the trajectory of an approachingvehicle has been identified by means of the displacement of itscorresponding unidirectional projections a speed of said vehicle isestimated and supervised so that it is possible to detect situations inwhich this approaching vehicle reduces speed and circulates at samespeed as said vehicle fitted with said device, staying at a shortdistance or vehicles circulating in different lanes at practically asame speed, and a specific type of alarm signal is emitted untilsubstantial changes are observed in an environment of said image of anapproaching vehicle.
 8. A method according to claim 6 wherein: said markcontrolled from a software that defines said image surface of interestis positioned in such a way that a car located in the overtaking lane ofa straight road and at a great distance is located in the left upper endof the mask, and the position of the mask with regard to the image canbe adjusted to get a fine adjustment of the field of vision.
 9. A methodaccording to claim 2, wherein in order to estimate an optical flow insaid one direction of an axis of a road a pair of successive images isprocessed and visual elements that are not moving forward are filteredand eliminated and in that said procedure is optional and may not beused.
 10. A method according to claim 7 wherein in case of a left turnof the motor vehicle constant displacement of visual elements containedin different images are detected in an upper portion of successiveimages by means of a correlations technique and coherence of said signalduring a number of successive images is used as an indication that avehicle fitted with the device is turning so that as the detection fieldmoves to a position closer to said vehicle more restrictive requirementsare imposed before activating said alarm signals.
 11. A method accordingto claim 7 and further additionally detecting whether said vehiclefitted with said device has initiated actions meaning an approach tosaid object.
 12. A method according to claim 11 wherein said indicativeactions comprise the activation of an indicator.
 13. A method accordingto claim 1 wherein said indicative actions comprise turning a steeringwheel.
 14. A method according to claim 1 wherein said alarm signalsinclude luminous signals of at least two colours, where each colourindicates a different warming level.
 15. A method according to claim 1wherein it further includes means for detecting drowsiness of the driverusing said detection device and emitting an alarm signal depending onthe relative position of the vehicle fitted with the detection device tothe lines marking the lanes on the road surface.
 16. A method accordingto claim 1, wherein said set of photosensor elements are integrated in adigital camera mounted in a rearview mirror of a vehicle and in thatsaid camera is positioned in such a way that: a left vertical edge ofsaid image surface is close to a side edge of a vehicle fitted with saiddevice; an upper edge of said image surface is lightly above the horizonline, by approximately one eighth of the image, said camera is slightlytilted in the clockwise direction so that it aligns said image surfacealong an axis of a road.
 17. An object presence detection device to putinto practice a method according to claim 1, said detection device beingof the type mounted to a motor vehicle, said vehicle having at least oneblind spot, where said detection device is for detecting an object suchan approaching vehicle situated in said blind spot and comprising: (a) areceiver (7) for detecting electromagnetic waves, said receiver (7)comprising a focusing device, and a light detector including a set ofactive photosensor elements that converts said electromagnetic wavesinto electrical signals, said light detector defining an image surface,(b) an electronic circuit (9) converting said electrical signals intodigitized signals, (c) a logic circuit (15) analyzing said digitizedsignals to analyze the presence of objects in said at least one blindspot which are moving relative to said vehicle, and generating variableoutput alarm signals depending on the result of said analysis, and (d)indicator members activated by said output signals, said detectiondevice being adapted to distinguish a vehicle from other objects,wherein said active photosensor elements are integrated in a digitalcamera, and said digital camera is positioned in such a way that: a leftvertical edge of said image surface is close to a side edge of a vehiclefitted with said device; an upper edge of said image surface is slightlyabove the horizon line, by approximately one eighth of the image, saidcamera is slightly tilted in the clockwise direction so that it alignssaid image surface along an axis of a road.
 18. A detection device asclaimed in claim 17, wherein said digital camera is housed in a vehicleexternal rear-view mirror unit.
 19. A detection device according toclaim 18, including a digital camera in each of said external rear-viewmirrors of said vehicle.
 20. A detection device as claimed in claim 18,wherein, a radius of action of said detection device is greater than 15m.
 21. A detection device, according to claim 20 wherein said detectiondevice has a radius of action greater than 20 m.
 22. A detection device,according to claim 17, wherein said electronic circuit (9) is of a CMOS,DMOS, MOS, Si-Ge or BiCMOS technology.
 23. A detection device accordingto claim 17, wherein said light detector is CMOS, DMOS, MOS, Si-Ge orBiCMOS technology.
 24. A detection device according to claim 17, whereinsaid electronic circuit (9) is SOI (silicon on insulator) technology.25. A detection device according to claim 17, wherein said lightdetector is SOI (silicon on insulator) technology.
 26. A detectiondevice according to claim 17, wherein it comprises a mask controlled bysoftware which allows to perform a partial selection of said activesensor elements so that said electronic circuit converts into digitisedsignals only electrical signals from said partial selected activephotosensor elements.
 27. A detection device according to claim 26wherein: said light detector is constituted by active sensor elementshaving a dynamic range equal or superior to six decades, i.e. between aminimum detection threshold value and a saturation threshold there is arange of six decades, with the light intensity being expressed in lux,on one same image surface; and one said sensor element has a dynamicrange equal or superior to the six decades, as defined above, betweentwo consecutive images.
 28. A detection device according to claim 27,wherein aid light detector comprises a two dimensional matrix of saidsensor elements defining a number of rows of sensor elements, where eachof said rows extends in a first direction and is parallel to theremaining rows, and where the group of rows forms said image surface,and each of said rows is provided with at the most 320 active sensorelements for processing the image and said light detector includes atthe most 256 active rows of sensor elements for processing forprocessing the image.
 29. A detection device according to claim 26wherein said logic circuit (15) comprises a specialized electroniccircuit including (a) a Von Neumann type sequential central processingunit (CPU), (b) a parallel coprocessor (TOT), specialized in thecalculation of a convolution over at least a portion of said imagesurface of the digitised signal, said coprocessor including at least 32partial accumulator multipliers with a high calculation speed forcalculating said convolution directly on the image surface at such acalculation speed that the convolution is completed before a new imageacquisition is initiated, and (c) a local RAM (SRAM).